Seriously non-linear feedback systems can exhibit chaotic behaviour. That may be what happened with your diesel engine. It is also surprisingly easy to create apparently simple mechanical systems which are chaotic, such as some compound pendulums.

The Pass paper you link to is notorious for denying that emitter/source/cathode degeneration is feedback (R4 in fig 9). Not to start that argument again here, but be aware that Nelson Pass is not mainstream however much his fans wish he were.

If this was the old days I would go to Garon records and say if you see Michale Gerzon ask him to pop in to see me ( one never visited him at home , he never answered the door ) . Alas I can not do that now . Describing a feedback amplifier is quite useful as a filter . I would elaborate about a problem I solved when using global feedback to illustrate the complexity of it . I wont , instead I will let Michael do it for me . Michael was in life very complex and shy . In print he was what I will never be , A master of English . Michael I suspect would outrank anyone here as a mathematician . If not the people who said so at Oxford were fools and the tax payer should be told .

Nelson Pass is doing what I do . He gives a picture . I notice he ducked controversial subjects in my link . Douglas Self is excellent especailly when describing two pole compensation . He shows why it should be distrusted and then it works . It works very well yet seldom is discussed . Very well , but not quite magic . I would imagine Scott would be one to ask ?

Self sometimes denies the emitter as feedback if a VAS . He got angry with me for using it . I wrote back and said " No it is to lift the base to help the current mirror " . Alas he had by then assumed I had thought of it as feedback " . I neither did , nor didn't . I did point out his current mirrors don't work properly , build them and you will see . If that VAS resistor is replaced by a diode things are not the same even if the DC conditions are the same ( easy ) . Makes me think Pass is right to have categories . I never fit diodes to cathodes for this reason . I do when getting going . Resistors are marginally cheaper . I don't fit transistor CCS to valves because my friends don't like it . I want to as they must be the very best . Using a LM337 as one is going too far .

BTW . Having Michael visit me at work was risking my job . My ex boss didn't like him . I recently phoned him about Michael . He was genuinely sorry and said he wished he had been nicer to him . In fact the two of them were very similar even down to their hidden origins ( Check , Jewish , my boss more the one who was hiding . Maxwell was another ) .

BTW . The diesel engine I described was an example of optimism . Very large diesel engines are almost as restricted as gas turbines except the revs are very different . For example the engine of a type 47 locomotive has from memory a rev range of about 100 RPM optimum ( circa 950 to 1100 ) . So what is that whistling sound as it leaves the station ? That is the turbo . The engineers kept increasing the turbo pressure . The chaotic failure was caused by that . The mechanism is not known , the cure is .

Electric generators and motors optimize the use of the power , the restricted rev range is not a problem .

I just noticed the PPI phone calls I get ( unwanted calls about insurance I never had ) are very distorted . It is like it is analogue . It must be digital ? Wonder why it has degraded ? It's the only exercise I get so don't care too much . Some friends get very heated about it . I can phone someone and get it stopped . I can not be bothered .

Distortion spectra, which starts out low , in the miliwatt range and then go high as power increases seems to fair better than those which starts out high then lowers as power is increased, in subjective listening test ..

Distortion spectra, which starts out low , in the miliwatt range and then go high as power increases seems to fair better than those which starts out high then lowers as power is increased, in subjective listening test ..

I had touched on this many moons back any additional thoughts ... ?

No additional thoughts. In the Mother Nature sounds reflected, or transferred, by any media, are more distorted the louder they are. And this distortions are heard as cues to the media, not as distortions. Like, you hear the wood, the stone, you hear sounds on the lake, in the bathroom, and so on. They are not heard as distortions. That's why distortions of electronic media if they follow similar pattern are not recognized as distortions.

In the Mother Nature sounds reflected, or transferred, by any media, are more distorted the louder they are. And this distortions are heard as cues to the media, not as distortions. Like, you hear the wood, the stone, you hear sounds on the lake, in the bathroom, and so on. They are not heard as distortions. That's why distortions of electronic media if they follow similar pattern are not recognized as distortions.

Instead of questioning the ability to hear distortions on low frequencies I would recommend them to check how their own speakers used in tests distort on that frequencies. Also, how flat is SPL dependence on frequency in their setup.